标准库排序和用户定义的类型 [英] Standard library sort and user defined types

问题描述

如果我想通过两种类型的变量之一对UDT的向量进行排序，标准库排序是否可以做到这一点，或者我需要编写自己的排序函数。

If I want to sort a vector of a UDT by one of two types of variables it holds, is it possible for the standard library sort to do this or do I need to write my own sort function.

例如，如果你有

struct MyType{
 int a;
 int b;
};

vector<MyType> moo;

// do stuff that pushes data back into moo

sort(moo.begin(), moo.end()) // but sort it by lowest to highest for a, not b

这是可能使用stdlib排序吗？谢谢。

So is this possible using the stdlib sort? Thanks.

推荐答案

如果你的类型实现bool operator< ...）const和一个复制构造函数（编译器生成或自定义）。

It is possible to use standard function if your type implements "bool operator < (...) const" and a copy constructor (compiler-generated or custom).

struct MyType {
    int a;
    int b;
    bool operator < (const MyType& other) const {
        ... // a meaningful implementation for your type
    }
    // Copy constructor (unless it's a POD type).
    MyType(const MyType &other)
        : a(other.a), b(other.b) { }
    // Some other form of construction apart from copy constructor.
    MyType()
        : a(0), b(0) { }
};

或者，您可以将排序函数（或函子）作为第三个参数传递给 sort（）而不是实现运算符<。

Alternatively, you can pass an ordering function (or a functor) as a third argument to sort() instead of implementing operator "<".

bool type_is_less(const MyType& t1, const MyType& t2) { ... }
...
std::sort(c.begin(), c.end(), type_is_less);

这在以下情况下很有用：

This is useful in the following situations:

1. 您不想因任何原因实施运算符 需要对内置或指针类型的容器进行排序，而不能对运算符进行重载。


2. 您希望使用不同顺序对序列进行排序。例如：有时你想要一个结构，第一/姓名成员按名字排序，其他时间按姓氏排序。两个不同的函数（或函子）使得这些选项不重要。

1. you don't want to implement operator "<" for whatever reason,
2. you need to sort a container of built-in or pointer types for which you can't overload operators.
3. you wish to sort the sequence using different orderings. ex: sometimes you want a struct with first/last name members sorted by first name, other times by last name. two different functions (or functors) make such options trivial.

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